Art of screw rolling



Ma 16, 1944. C, R cH D 2,348,850

ART OF SCREW ROLLING Original Filed May 3, 1939 ulnumunn mmugmmufl 1.9 W 12 10 2a 'INV'ENT'OR Cecz'' BY a M MM ATTORNEYS Patented May 16, 1944 ART OF SCREW ROLLING Cecil C. Richards, Union City, N. J., assignor to Groov-Pin Corporation, Union City, N. J., a corporation of New York Original application May a, 1939, Serial No. 271,472. Divided and this application October 17, 1941, Serial No. 415,356

7 Claims.

The present invention is concerned with methods and apparatus for producing screws and particularly selhcutting screws by a rolling operation.

Among the objects of the invention are to provide a method by which the rolling operation may be performed expeditiously without the unobjectionable burrs or unevenness, but with particularly clean and sharp cutting edges and without injury to or deformation of the screw threads or the segments thereof traversed by the cutting grooves.

Another object is to provide rolling dies for carrying out the method of the invention, which shall be of simple and relatively inexpensive construction.

In the accompanying rawing in which is shown one of various possible embodiments of the several features of the invention.

Fig. l is a perspective view showing the general relationship of coacting die plates of the inven tion by which the method may be executed,

Fig. 2 is a plan View of that die plate which has the cutting groove rolling element,

Fig. 3 is a side elevation of said die plates,

Fig. 4: is a transverse sectional view of the'die, taken on line S-d of Fig. 1, and,

Fig. 5 is a side elevation of the resultant screw product.

Referring now to the drawing, the die includes a thread rolling die plate A which has low-pitch parallel ribs it over the entire area thereof, that are of the conventional construction usual in thread rolling dies. Desirably the die plate A includes a formation to roll a pilot upon the screw blank. To this end the ribs are elevated progressively toward one lateral edge of the die plate shown in Fig. 4. If desired, the peaks of the ribs that would otherwise protrude above the main level of the die plate are levelled off flush therewith as shown at I2. The pilot formation of the die plate may be produced in any of various ways available to those skilled in the art, illustratively by the method disclosed in the parent application, Serial No. 271,472, filed May 3, 1939, of which this case is a division, and which has resulted in Patent No. 2,276,875, dated March 17, 1942.

The complementary die plate B has thread rolling ribs I3, generally conventional in construction, but includes also the cutting groove rolling element. This element desirably com-- prisesv an. insert die plate M affixed in a corresponding rectangular notch l 5 in one lateral face cf the die plate and spaced from both ends thereof, as shown. The insert die plate I4 is securely afiixed with respect to the main die plate by clamping the same in place in a manner Well known to those skilled in the art. The ribs 9 of the element hiin said die plate B are steep, as best shown in Figs. 1 and 2. They are of height greater than and preferably 10 to 20 per cent greater than the height of the thread rolling ribs l3.

Preferably the section iii of the die rolling plate B, as shown i Fig. 2, has a length of at least three times the pitch circumference of the screw to be rolled. The cutting groove insert die section It is of length preferably not less than twice the pitch circumference of the screw to be rolled, while the section il shown at the left end of the die plate in Fig. 2 is desirabiy of length no less than one complete pitch circle of the screw to be rolled.

In operation, the cylindrical rod stock from which the screw is to be rolled, whether headed or not is passed in conventional manner between the two die elements A and B. In this operation, the section Iii as it passes along the companion die plate A rolls a complete thread upon the length of the shank and at the same time reduces the entry end thereof to form the pilot. By the time the section it has rolled over the rod, the threads will have been completely formed. As the operation proceeds, the section iii of the die plate B continues, by its cooperatio with the companion die plate A, to roll the thread and to position the screw blank against displacement, while the ribs IS of the insert die plate It impress the cutting grooves across the pilot end of the screw. In this displacement of metal of the previously formed screw threads it is apparent that burrs and irregularities are necessarily formed at the cutting edges and these would greatly impair the cutting efficacy of the screw.

According to the present invention, the final section ll of the die plate B, going into action after the cutting grooves have been formed, serves effectively by its cooperation with the companion die plate A to roll or smear the excess metal or burrs into the surface of the screw and thereby to produce a clean screw product which will efficiently cut its thread into the stock to which it is tobe applied.

Where the pressure exerted by the die upon the screw is maintainedv clear to the extremity of the rolling operation, the screw might become deformed in cross-section by the sudden release of the die pressure thereon and notches or other imperfections might appear across the threads.

It is accordingly another feature of the present invention to modify one of the die plates near the release end thereof for progressive increase of the distance of its ribs at such release end from the companion die plate. Preferably this release is such that at the discharge extremity of die plate A the distance from the companion plate B has been increased by ap-, proximately the thread height of the screw being rolled. The required relief or sloping conformation, illustratively of the rolling faces of die plate A is shown at 20. It may be produced in any of the manners known to those skilled in the art, for instance, in the manner shown in the parent application, above identified.

From the foregoing description of the operation of the particular die equipment set forth the method of rolling the screw will be understood. It may be briefly stated that this method consists in first rolling the complete thread conformation upon the screw blank, thereupon rolling the steep cutting grooves across and to interrupt the threads, and finally resuming the thread rolling operation and thereby cleaning up burrs or irregularities. In the latter step, preferably the pressure upon the screw is progressively reduced as the cleaning up operation proceed, until there is substantially no pressure upon the screw as the operation is about to conclude.

The screw shown in Fig. 5 is one illustrative example of the product produced by the method and apparatus of this invention. The threads 2| about the shank extend clear to the entry end of the screw, at which end the shank is shown reduced in diameter to afford a pilot 22. The cutting grooves transversely of the threads appear at 23 and extend in this embodiment for the length of the pilot.

It will be understood that the method described could be executed by apparatus other than that set forth, for instance by two or three distinct sets of dies, one to perform the thread rolling, one to perform the grooving and the final set to perform the burr removing or cleaning up operation. It is also apparent that either the initial thread rolling operation or the final burr removing or cleaning up operation could be performed by a die equipment separate and distinct from the die equipment which performs both of the other operations.

While the drawing shows equipment for producing a screw with a reduced pilot, it will be understood that the invention could be carried out upon a screw of shank diameter uniform from end to end. It will also be understood that the length of the cutting grooves may be varied depending upon the width of the insert die plate I4.

As many changes could be made in the above method and apparatus and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

1. The method of rolling a self-cutting screw, which consists in rolling uninterrupted threads which comprises rolling threads along the screw shank in one continuous operation by impression of the threads concurrently into diametrically opposed parts of the rolling shank and after continuous threads have been completely formed but in the course of the thread rolling operation rolling steep cutting grooves along the screw shank, traversing and deeper than the threads, and after completion of the rolling of said cutting grooves resuming the initial thread rolling operation.

3. The method of rolling a self-cutting screw, which consists in first rolling uninterrupted threads about the shank thereof by impression of the threads concurrently into diametrically opposed parts of the rolling shank, thereupon rolling cutting grooves deeper than said threads at a steep angle from the entry end of the shank and finally resuming the initial thread rolling operation and thereby cleaning up any unevenness of burrs produced in the cutting groove rolling, while gradually releasing the pressure exerted upon the screw at the conclusion of the rolling operation.

4. Thread rolling apparatus comprising a pair of complementary thread rolling die plates, one of said plates having parallel oblique ribs of low pitch, the complementary die plate having corresponding ribs at the inlet segment and at the release segment thereof and having interposed between said segments, a section with ribs extending at high pitch, with their tops at level higher than those of the other ribs, whereby in rolling operation, the initially rolled thread is interrupted by grooves pressed into the screw transversely of the threads, and in the final part of the thread rolling operation unevenness and burrs produced by the grooving section are cleaned up.

5. The combination recited in claim 4 in which the outlet or release end of one of the die plates is relieved to a degree corresponding approximately to the height of thread being rolled.

6. The combination recited in claim 4 in which the groove forming portion of the complementary die plate is a rectangular insert spaced from both ends of said plate and extending from one longitudinal edge of the die for part of the width of the die to interrupt the thread forming for only the corresponding part of the length of the screw shank, and in which the thread forming ribs extend over the entire area of the face of the die plate other than that occupied by the insert.

7. The combinaiton recited in claim 4 in which the segment at the inlet of the complementary thread rolling die plate is of length approximately three times the pitch circumference of the screw to be rolled, in which the interposed section is of length no less than twice the pitch circumference of the screw to be rolled and the thread rolling section beyond said interposed section is of length no less than one complete pitch circle to be rolled.

CECIL C. RICHARDS. 

